I made available a pdf file containing a short introduction to ordinary differential equations. These notes (or booklet, if you prefer) build a model from a given problem, reaching its mathematical formulation (which, of course, involves in an essential way an ordinary differential equation), discussing also many critical aspects found "on the road". These notes are the result of a long and varied experience in teaching...
Who wants, can download it: Differential Equations: intro.

Enjoy!
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